The present invention relates generally to a system for cleaning printheads and more particularly to a service station and method for cleaning inkjet printheads.
Inkjet printheads are widely used and well known in the art. One type of inkjet printhead is based on drop-on-demand systems that use either piezoelectric or thermal printhead technologies.
In high-resolution drop-on-demand inkjet printing, very small ink droplets are ejected through tiny apertures in a nozzle plate. Contaminants, such as dust particles and paper fibers, tend to accumulate in the vicinity of these apertures, interfering with the ejection of the ink droplets. In addition, modem ink formulations contain, among other components, pigments, resins, and fast drying accelerators When the printer is not in use, these components, particularly pigments, have a tendency to dry out, blocking the nozzle apertures of the printhead. In addition, they can become so hard that they scratch the face of the nozzle plate, degrading inkjet accuracy.
In order to avoid accumulation of ink residues, dust and print fibers when the printhead is not in use, service stations are installed in printing machines. These stations periodically clean the nozzle plate of the printheads, removing contaminants and residues.
Many types of service stations are known in the art. Usually, during periods of non-use, the service stations cap the system, sealing the nozzles from contamination and drying. Some capping systems also facilitate priming of the printhead by drawing a vacuum on the printhead. During maintenance, many service stations cause ejection of a number of ink drops through each of the nozzle apertures of the printhead. The droplet ejection process is known as spitting and the ejected ink is collected in a spittoon that is part of the service station.
Most service stations use an elastomeric wiper that wipes the nozzle plate and removes ink residues, paper dust and other debris that have collected during use. An example of such a service station is disclosed in PCT Patent Publication WO 9615908. In ""908, the cleaning and sealing station has among other features, a wiper, a sealing cap, and a suction element for withdrawing excess ink.
Other approaches or refinements to maintaining a clean nozzle surface on inkjet printheads are discussed in U.S. Pat. Nos. 6,786,830 and 5,815,176. The former teaches a station which uses a wiper with an adaptive wiping speed while the latter describes the use of a multi-finned wiping system.
The present invention describes a method for cleaning the nozzle plate of printheads by using at least one sprayer to spray a liquid cleaning agent onto a nozzle plate prior to wiping. The sprayed agent improves the efficiency of cleaning in several ways. It thins any liquid ink left on the nozzle plate and dissolves solid pigment residue stuck to the plate. It decreases the drying rate of fast drying inks and acts as a lubricant for the wiper, generally preventing scratches.
The present invention teaches a service station system for cleaning a printhead that includes a translational means for bringing the service station into proximity with the printhead. It also includes a cleaning agent means for distributing a cleaning agent over a printing face of the printhead when the service station is in proximity with the printhead. Finally, the system includes a wiper for wiping the cleaning agent off the printing face.
The translational means can either translate the service station with respect to the printhead or vice versa. Similarly, the translational means can translate the printhead with respect to the wiper or vice versa.
In an embodiment of the present invention, the cleaning agent means for distributing a cleaning agent is at least one sprayer.
In one embodiment the service station system can be used with an inkjet printhead.
The service station system uses cleaning agents, where the agents remove at least one of the following materials from a group consisting of ink, ink components, dust particles, and paper fibers.
The present invention also teaches a method for cleaning a printhead including the step of distributing a cleaning agent over a printing face of the printhead.
In one embodiment the present invention teaches a method for cleaning a printhead where the method includes spraying a printing face of a printhead with a cleaning agent.
In another embodiment, the invention teaches a method which includes the steps of bringing a service station into proximity with a printhead, spraying a printing face of a printhead with a cleaning agent; and lowering the service station to a level where a wiper of the service station wipes the printing face.
In yet another embodiment, the method for cleaning a printhead further includes the steps of pressing the service station to the printhead and effecting a vacuum. The vacuum causes ink to be discharged from nozzles in the printhead. Finally the method may also include the step of suctioning off the ink that has been discharged. The steps of pressing and suctioning are effected generally prior to the spraying step.